This invention relates to a circuit arrangement for supplying a discharge lamp, comprising
a converter for generating a high-frequency current at a frequency f from a supply voltage, and PA1 a circuit portion I for adjusting the power consumed by the discharge lamp through adjustment of the frequency.
The invention also relates to a compact fluorescent lamp and to a method of supplying a discharge lamp.
A circuit arrangement as mentioned in the opening paragraph is known from U.S. Pat. No. 5,003,230. In the known circuit arrangement, an inductive element is connected in series with the discharge lamp. If the frequency f is made higher, the impedance of the inductive element increases, so that the lamp current decreases. It is thus possible to dim the discharge lamp by means of the known circuit arrangement in that the frequency is adjusted by means of the circuit portion I. A disadvantage of supplying a discharge lamp with a high-frequency current is that, for example, in the case of a low-pressure mercury discharge lamp, striations may arise in the discharge lamp, especially if the discharge lamp operates in the dimmed state. A further disadvantage is that there is no unequivocal relation between the power consumed by the discharge lamp and the frequency f, especially for comparatively low luminous flux values and comparatively low ambient temperatures. As a result of this, the luminous flux of the discharge lamp will fluctuate in time, a phenomenon which is usually referred to as "moding". A problem which also arises in this dimming method is that the color point of the light radiated by the discharge lamp lies comparatively far removed from the blackbody line in the color triangle during dimming.